The Internet Protocol (IP) has become established for providing multimedia services over telecommunications networks. The IP Multimedia Subsystem (IMS) is the technology defined by the Third Generation Partnership Project (3GPP) to provide IP Multimedia services over mobile communication networks. IP Multimedia services provide a dynamic combination of voice, video, messaging, data, etc. within the same session.
The IMS makes use of the Session Initiation Protocol (SIP) to set up and control calls or sessions between user terminals. SIP signals use the Session Description Protocol (SDP) to describe and negotiate the media components of the session. Whilst SIP was created as a user-to-user protocol, the IMS allows operators and service providers to control user access to services and to charge users accordingly.
FIG. 1 illustrates schematically how the IMS fits into the mobile network architecture in the case of a General Packet Radio Service (GPRS) access network. As shown in FIG. 1 control of communications occurs at three layers (or planes). The lowest layer is the Connectivity Layer 1, through which signals are directed to/from client user equipment, UE, accessing the network. A gateway GPRS support node (GGSN) 2 acts as an interface between the GPRS backbone network and other networks (radio network and the IMS network). The middle layer is the Control Layer 4, and at the top is the Application Layer 6.
The IMS 3 includes a core network 3a, which operates over the middle, Control Layer 4 and the Connectivity Layer 1, and a Service Network 3b. The IMS core network 3a includes nodes that send/receive signals to/from the GPRS network via the GGSN 2a at the Connectivity Layer 1 and network nodes that include Call/Session Control Functions (CSCFs) 5, which operate as SIP proxies within the IMS in the middle, Control Layer 4. The top, Application Layer 6 includes the IMS service network 3b. Application Servers (ASs) 7 are provided for implementing IMS service functionality.
FIG. 1 also shows a Content Storage Layer 8, which includes servers that store data, referred to as “content”. Some applications may be configured such that a user can request provision of content information from one of these content servers. The user may be informed that the information content is available from a server at a particular location. This information content is referred to as in-directed content, and the server is referred to as a Content Server. The Content Server may be at any location accessible over the internet. In these cases, it is left to the individual user to decide if and when to request retrieval of the content. The method of informing the user is to send a message to the user with an indication that the information is available together with the location from which it can be retrieved. This approach is useful when the data itself may be quite large (e.g. when the information includes multimedia data such as icons, media files etc.).
An example of where in-directed content may be used is in Presence and List Management services. A Presence service allows a user to subscribe to presence information so as to be able to see if other users are available and willing to communicate. A user's presence information (presence state) may include, for example, whether or not they are on-line, whether or not they are busy or willing to communicate, or their geographical location. An AS, referred to as a Presence Server controls the presence service. A user who provides presence information to a presence service is referred to as a presence entity, or presentity, while a user who is kept informed about the presence states of other users is referred to as a watcher. To control the watchers that are permitted to see the presence state of a presentity, and the presence states that any particular watcher is permitted to see, a set of authorization rules is maintained, to which the presence server can refer. These rules include a list of the users who are authorized to be watchers for each presentity. The authorization rules are maintained in an XML document by an XML Document Management Server (XDMS).
Many Presence services in use today employ the SIMPLE based solution defined by IETF, and used by 3GPP and the Open Mobile Alliance (OMA). Content in-direction is often used for large multimedia data. When the presence state of a presentity changes, this information content is provided to the content server by the presentity, and then a link to that content is included in presence data that is sent (published) to the presence server. The presence server then notifies all concerned and authorised watchers about the change of presence data and the watcher fetches the information from the content server, pointed out by the link included in the presence data.
Before the information is provided to the watcher, it is necessary to verify that the watcher is authorised to receive the information. However, there is currently no standard way to verify authorize that the watcher is authorised when fetching the information from the content server. Consequently, presence service providers each use their own, more or less complex and proprietary solution to make sure that the watcher is authorised to see the data.
The present invention has been conceived with the foregoing in mind.